JP2015055544A - Wavefront measurement instrument, wavefront measurement method, method of manufacturing optical element, and assembly adjustment device of optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavefront measurement instrument which is capable of wavefront measurement of an optical element having large wavefront aberrations, has high accuracy, and is low-cost.SOLUTION: The wavefront measurement instrument measures a transmitted wavefront or a reflected wavefront of an optical element and includes: measurement means which measures a light intensity distribution on the basis of a luminous flux transmitted through or reflected by the optical element; area determination means which determines a first area and a second area on the basis of a plurality of spot positions in the light intensity distribution; first signal processing means which calculates a first wavefront using a linear model on the basis of information relating to a light intensity distribution in the first area; and second signal processing means which estimates a second wavefront by repeating light propagation calculation with the first wavefront as an initial value on the basis of information relating to light intensity distributions in the first area and the second area.

Description

  The present invention relates to a wavefront measuring apparatus that measures a transmitted wavefront or reflected wavefront of an optical element.

  The imaging optical system includes optical elements such as a mirror and a lens, an optical unit that combines these elements, and the like. Before assembling the imaging optical system, the performance of each optical element or each optical unit can be guaranteed by measuring the transmitted wavefront or reflected wavefront (test wavefront) of each optical element or each optical unit. Non-Patent Document 1 discloses a Shack-Hartmann wavefront sensor (SHWFS) for measuring a transmitted wavefront (test wavefront).

  However, when the displacement of the test wavefront increases, it becomes difficult or impossible to reconstruct the test wavefront using SHWFS. Therefore, Non-Patent Document 2 discloses a method using correction lenses (Compensators) for correcting the displacement of the wavefront to be detected within the dynamic range that can be measured by the wavefront measuring sensor. Thereby, it is possible to cope with a case where the displacement of the wavefront to be detected is large.

Daniel Malacara, “Optical Shop Testing”, Third Edition, Wiley-Interscience, p. 383-386 Eric P. Goodwin and James C.I. Wyant, “Field Guide to Interferometric Optical Testing (Spie Field Guides)”, SPIE Press, p. 79

  However, as disclosed in Non-Patent Document 2, when the displacement of the wavefront to be detected is corrected within the dynamic range of the wavefront measurement sensor using the correction lens, the measurement due to the posture error or shape error of the correction lens is performed. Uncertainty increases. In addition, the correction lens needs to be designed and manufactured with high accuracy, and much time and cost are required to prepare the correction lens. In addition, since a correction lens corresponding to the optical system to be measured is required, when the type of optical system to be measured increases, the type of correction lens also increases and the cost of wavefront measurement increases.

  Accordingly, the present invention provides a wavefront measuring apparatus, a wavefront measuring method, an optical element manufacturing method, and an optical system assembly adjustment apparatus that are capable of measuring a wavefront of an optical element having a large wavefront aberration and that are highly accurate and low cost. provide.

  A wavefront measuring apparatus according to one aspect of the present invention is a wavefront measuring apparatus that measures a transmitted wavefront or a reflected wavefront of an optical element, and measures a light intensity distribution based on a light beam transmitted or reflected by the optical element. A region determination means for determining the first region and the second region based on a plurality of spot positions in the light intensity distribution, and a linear model based on information on the light intensity distribution of the first region. Based on the first signal processing means for calculating the first wavefront and the information on the light intensity distribution of the first region and the second region, the light propagation calculation is performed using the first wavefront as an initial value. Second signal processing means for estimating the second wavefront by repeatedly performing the processing.

  A wavefront measuring method as another aspect of the present invention is a wavefront measuring method for measuring a transmitted wavefront or a reflected wavefront of an optical element, and measuring a light intensity distribution based on a light beam transmitted or reflected by the optical element. Determining a first region and a second region based on a plurality of spot positions in the light intensity distribution, and using a linear model based on information on the light intensity distribution of the first region. Calculating the wavefront of the first wavefront, and repeating the light propagation calculation using the first wavefront as an initial value based on the information on the light intensity distribution of the first area and the second area. Estimating a wavefront.

  The method for manufacturing an optical element according to another aspect of the present invention uses the wavefront measuring method.

  An optical system assembly adjustment apparatus according to another aspect of the present invention calculates an arrangement position or orientation of the optical element using the wavefront measurement method, and assembles the optical system based on the arrangement position or orientation. Make adjustments.

  Other objects and features of the present invention are illustrated in the following examples.

  According to the present invention, a wavefront measurement of an optical element having a large wavefront aberration is possible, and a highly accurate and low-cost wavefront measurement apparatus, a wavefront measurement method, an optical element manufacturing method, and an optical system assembly adjustment apparatus Can be provided.

It is a principal part block diagram of the wavefront measuring apparatus in Example 1. FIG. It is a schematic diagram when a reference wavefront is incident on a Shack-Hartmann wavefront sensor (SHWFS). It is a schematic diagram when a test wavefront is incident on a Shack-Hartmann wavefront sensor (SHWFS). It is a schematic diagram when a test wavefront having a large aberration is incident on a Shack-Hartmann wavefront sensor (SHWFS). It is a figure which shows an example of the output signal from a detector array in the case of injecting a to-be-measured wavefront with large aberration. 2 is a block diagram of a signal processing unit in Embodiment 1. FIG. In Example 1, it is explanatory drawing of the gravity center detection area | region of a spot image. 6 is a schematic diagram of the inclination of a light beam incident on an encoding optical system (Shack-Hartmann wavefront sensor) in Embodiment 1. FIG. In Example 1, it is a figure which shows average incident angle error (DELTA) (theta) at the time of detecting a gravity center in two mutually different area | regions in Example 1. FIG. In Example 1, it is explanatory drawing of the area | region which can recover a wavefront with high precision. FIG. 10 is a block diagram of another form of signal processing unit according to the first exemplary embodiment. It is a principal part block diagram of the wavefront measuring apparatus in Example 2. FIG. It is a principal part block diagram of the wavefront measuring apparatus of another form in Example 2. FIG. It is a principal part block diagram of the wavefront measuring apparatus in Example 3. It is a principal part block diagram of the wavefront measuring apparatus in Example 4. It is a principal part block diagram of the wavefront measuring device of another form in Example 4. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In each figure, the same members are denoted by the same reference numerals, and redundant description is omitted.

  First, the wavefront measuring apparatus according to the first embodiment of the present invention will be described. FIG. 1 is a configuration diagram of a main part of a wavefront measuring apparatus 100 according to the present embodiment. The wavefront measuring apparatus 100 is configured to measure a transmitted wavefront or a reflected wavefront of a test optical system (optical element).

  In the wavefront measuring apparatus 100, the light beam LB from the light source LS enters the illumination optical system ILO. The illumination optical system ILO shapes the light beam LB into a desired light beam LB1. For example, the illumination optical system ILO can expand divergent light from a fiber or a pinhole into a light beam LB1 that only covers the measurement region of the optical system TO (measurement target optical element). The illumination optical system ILO can also adjust the amount of light and the polarization state using an ND filter and a polarizing filter. The light beam LB1 shaped by the illumination optical system ILO enters the test optical system TO. The light beam LB1 passes through the test optical system TO and becomes the test light beam LB2.

  The relay optical system RYO causes the test light beam LB2 transmitted through the test optical system TO to enter the encode optical system and form a spatially modulated light intensity distribution. In this embodiment, a Shack-Hartmann sensor optical system SH (Shack-Hartmann wavefront sensor) including a lenslet array MLA and a detector array DA (two-dimensional detector array) is used as an encoding optical system (measurement means). However, the present embodiment is not limited to this.

  The light (test light beam LB2) irradiated on the lenslet array MLA forms a spot image IS corresponding to the inclination of the wavefront on the detector array DA. The spot image intensity distribution formed on the detector array DA is output as a spot image IS (intensity distribution data) through photoelectric conversion and AD (Analog to Digital) conversion by the detector array DA. The signal processing unit DSP performs wavefront recovery processing on the spot image IS (intensity distribution data) output from the detector array DA, and outputs a measurement wavefront WM.

  In a conventional Shack-Hartmann wavefront sensor (SHWFS), these relationships are modeled as a linear problem in order to reconstruct the wavefront from the spot image IS. Here, the wavefront reconstruction algorithm in the conventional SHWFS will be described. FIG. 2 is a schematic diagram when a reference wavefront is incident on SHWFS. FIG. 3 is a schematic diagram when the wavefront to be detected is incident on the SHWFS.

First, as shown in FIG. 2, the reference wavefront W0 is made incident on the lenslet array MLA in a state where the test optical system TO is not provided, and the reference spot position RSP (x _{r 1} , y _r ) are obtained in advance. As the reference wavefront W0, a known plane wave, a divergent spherical wave generated from a point light source, or the like can be used.

Thereafter, as shown in FIG. 3, the wavefront W1 to be measured is incident on the lenslet array MLA, and the measurement spot position MSP1 (x _t , y _t ) is obtained. The measurement spot position MSP1 can be calculated as a spot center position using an algorithm such as centroid detection for the spot formed by each lenslet. Then, the displacement of the spot position MSP1 by the wavefront W1 to be detected with respect to the reference spot position RSP is obtained.

  Here, it is assumed that the lenslet is a thin lens, and the spot center position is assumed to be the intersection of the light beam passing through the center of the lenslet and the detector array DA surface. Thereby, the inclination of the wave front can be obtained geometrically. Specifically, based on the displacement of the spot center position and the distance between the lenslet array MLA and the detector array DA, the average inclination of the wavefront incident on one lenslet constituting the lenslet array MLA is calculated. Can be sought. The wavefront corresponding to one microlens is obtained for all the microlenses, and the average inclination of the wavefront incident on one microlens is approximated to the inclination of the wavefront at the center of the lenslet to integrate the wavefront inclination. Thereby, the wavefront on the lenslet array MLA can be reconstructed.

However, in this conventional SHWFS wavefront reconstruction algorithm, when the inclination of the wavefront to be detected becomes large, the spot on the detector array DA becomes dense, and the accuracy of spot center detection decreases due to the detection of the center of gravity due to the influence of adjacent spots. To do. Further, the accuracy of spot center detection also decreases when the spot on the detector array DA extends or deforms. If the inclination of the wavefront to be detected is further increased, spots may overlap and the wavefront may not be reconstructed. FIG. 4 is a schematic diagram when a large aberration wavefront is incident on SHWFS. As shown in FIG. 4, when the wavefront to be detected W2 having a wavefront displacement larger than the wavefront W1 to be detected is incident on the lenslet array MLA, a plurality of spots intersect at the measurement spot position MSP2 (x _t , y _t ). End up. For this reason, it is impossible to identify which lenslet of the lenslet array MLA is a certain spot.

  FIG. 5 is a diagram illustrating an example of an output signal from the detector array DA when a wavefront to be detected having large aberration is incident. That is, FIG. 5 is an example of the spot image IS obtained when the wavefront transmitted through the test optical system TO is incident on the Shack-Hartmann sensor optical system SH. Since the test optical system TO has a large spherical aberration, spots are overlapped on the outer peripheral portion of the spot image IS. In this case, with the conventional SHWFS wavefront reconstruction algorithm, it is difficult to perform wavefront reconstruction in this region (outer peripheral portion).

  Here, with reference to FIG. 6, a description will be given of a wavefront recovery algorithm performed by the signal processing unit DSP of the present embodiment when spots overlap. FIG. 6 is a block diagram of the signal processing unit DSP in the wavefront measuring apparatus 100. As shown in FIG. 6, the wavefront W (test wavefront) of the test optical system TO is incident on the encode optical system 120 (measurement means). The encoding optical system 120 measures the light intensity distribution (spot image IS) based on the light beam transmitted or reflected by the optical element. That is, the encoding optical system 120 generates a light intensity distribution (spot image IS) including information on the wavefront to be detected (the transmitted wavefront or the reflected wavefront of the optical element), and outputs the spot image IS to the signal processing unit DSP. In this embodiment, a case where a Shack-Hartmann sensor optical system SH is used as the encoding optical system 120 will be described.

  The wavefront recovery region determination unit 201 (region determination unit) of the signal processing unit DSP determines a region where wavefront recovery is possible by the SHWFS wavefront reconstruction algorithm based on the input spot image IS. In other words, the wavefront recovery region determination unit 201 performs the first region (region 1) and the second region (on the basis of a plurality of spot positions (spot positions included in the regions L1, L2) in the light intensity distribution (spot image IS) Determine area 2). Specifically, for example, at a spot near the center of the spot image IS, a lenslet that forms the spot is first obtained. Subsequently, the center of gravity is detected in each of the regions L1 and L2 at spots adjacent to each other toward the outer peripheral portion of the spot image IS. As described above, the wavefront recovery region determination unit 201 uses the first region (region 1) and the second region based on the plurality of spot positions detected in a plurality of detection regions (regions L1 and L2) having different sizes. A region (region 2) is determined.

  FIG. 7 is an explanatory diagram of the center-of-gravity detection region of the spot image IS (enlarged view of the spot image IS), and shows a region L1 and a region L2 in the spot S1 near the outer periphery of the spot image IS. The region L2 is a region inside a dotted square surrounding the spot S1. The region L1 is a region inside a solid square larger than the region L2, and is a region including the region L2. As shown in FIG. 7, the center of gravity of each of the regions L1 and L2 is detected for each of the spots S1 to S14 at the outermost peripheral portion of the spot image IS.

  In the spot S1, the influence of the adjacent spot is small because the distance from the adjacent spot is sufficiently long. For this reason, the centroid detection results (centroid detection positions) in the regions L1 and L2 are substantially the same (no substantial difference occurs). On the other hand, for example, in an area outside the spot S14, that is, in an area away from the center of the spot image IS (spots S8, S12, S13, S14, etc.), the interval between adjacent spots is reduced, or adjacent spots overlap each other. For this reason, a difference occurs in the center of gravity detection result (center of gravity detection position) in each of the region L1 and the region L2.

  Here, the influence which the difference of the gravity center detection position in each of the area | region L1 and the area | region L2 has on wavefront measurement is considered. Using the SHWFS wavefront reconstruction algorithm, the average inclination (wavefront slope) of the wavefront incident on one lenslet constituting the lenslet array MLA is obtained. The wavefront slope is calculated based on the displacement of the spot center position from the reference position and the distance between the lenslet array MLA and the detector array DA.

FIG. 8 is a schematic diagram of the inclination of the light beam incident on the encoding optical system 120 (Shack-Hartmann sensor optical system SH). Reference spot position _(x r, _{y r)} measurement spot position relative to _(x t, _{y t)} displacement _{(x t -x r, y t} -y r), and, between the lenslet array MLA and the detector array DA Is used to calculate the wavefront slope β as shown in the following equation (1).

In equation (1), w is the wavefront shape, and k is the index number of each lenslet.

When a difference between the spot centroid detection position ( _{xt, L1} , yt _{, L1} ) in the region _L1 and the spot centroid detection position ( _{xt, L2} , yt _{, L2} ) in the region L2 occurs, this difference The wavefront slope error Δβ is expressed by the following equation (2).

  Furthermore, as represented by the following equation (3), the wavefront slope error Δβ can be converted into an average incident angle error Δθ.

  In order to reconstruct the wavefront with high reproducibility using the SHWFS wavefront reconstruction algorithm, it is necessary that the average incident angle error Δθ calculated from the centroid detection position in each of the regions L1 and L2 is sufficiently small. For example, consider the case of the Zernike polynomial focus component term Z4. At this time, if the coefficient of Z4 is C4, the wavefront shape of the focus component term Z4 is expressed as the following equation (4).

In Expression (4), r is a normalized radius.

  At this time, the relationship between the average incident angle error Δθ and the error ΔC4 of the coefficient C4 (Zernike coefficient) is expressed by the following equation (5).

In equation (5), r is the wavefront analysis radius. In general wavefront measurement, at least the error ΔC4 (Zernike coefficient error) needs to be about 50 nm or less. For this reason, when the wavefront analysis radius r is 2 mm, the average incident angle error Δθ allowable at the outermost circumference of the analysis radius is about 0.1 mrad or less.

  FIG. 9 is a diagram showing an average incident angle error Δθ when the center of gravity of each spot (spots S1 to S14) is detected in detection areas (areas L1 and L2) having two different sizes. FIG. 9 shows a case where the area L2 is set to an area of 19 pixels × 19 pixels and the area L1 is set to an area of 21 pixels × 21 pixels in the spot image IS (intensity distribution data) of FIG. FIG. 9 shows the calculation result of the average incident angle error Δθ in the lenslet array MLA corresponding to each of the spots S1 to S14.

  At this time, the size of one pixel (pixel) of the detector array DA is 4.65 μm × 4.65 μm. The distance L between the lenslet array MLA and the detector array DA is 3.7 mm. As shown in FIG. 9, spots whose average incident angle error Δθ is unacceptable (that is, 0.1 mrad or more) are spots S8 to S14. When the SHWFS wavefront reconstruction algorithm is used in this embodiment, as shown in FIG. 10, the first region (region 1) in which the wavefront reconstruction can be performed with high accuracy and the error of the wavefront reconstruction are allowable values. It can be separated into a second region (region 2) exceeding.

  As described above, the wavefront measuring apparatus 100 (signal processing unit DSP) of the present embodiment performs centroid detection in detection areas (areas L1 and L2) having two different sizes, and determines the difference between the detected two centroid positions. Based on this, the wavefront error of each lenslet is evaluated. Accordingly, the signal processing unit DSP can determine the wavefront recovery region using the SHWFS wavefront reconstruction algorithm. That is, the signal processing unit DSP can appropriately separate the first area (area 1) where the wavefront recovery can be performed with high accuracy and the second area (area 2) where the wavefront recovery error is large.

  As described above, the signal processing unit DSP (wavefront recovery region determination unit 201) illustrated in FIG. 6 determines the first region (region 1) where the wavefront recovery can be performed with high accuracy. Then, the wavefront reconstruction unit 202 (first signal processing unit) of the signal processing unit DSP uses the linear model based on information on the light intensity distribution (spot image IS) of the first region (region 1). 1 wavefront (measurement wavefront WM1) is calculated. That is, the wavefront reconstruction unit 202 calculates the measurement wavefront WM1 of the region 1 using the Shack-Hartmann wavefront recovery algorithm based on the spot position (spot center position) obtained by detecting the center of gravity in the region 1. Preferably, the wavefront reconstruction unit 202 calculates the first wavefront using geometric optical calculation.

  Subsequently, the wavefront estimation unit 203 (second signal processing unit) performs the second operation based on the measured wavefront WM1 calculated by the wavefront reconstruction unit 202 and the spot image IS from the wavefront recovery region determination unit 201. The estimated wavefront WM2 of the region (region 2) is calculated. That is, the wavefront estimation unit 203 initializes the first wavefront (measured wavefront WM1) based on the information (spot image IS) regarding the light intensity distribution of the first region (region 1) and the second region (region 2). The light propagation calculation is repeated as a value to estimate the second wavefront (estimated wavefront WM2). In this embodiment, the estimated wavefront WM2 is calculated using an estimation method such as a maximum likelihood method. Preferably, the wavefront estimation unit 203 estimates the estimated wavefront WM2 using wavefront parameter optimization calculation.

  Then, the wavefront calculation unit 204 (third signal processing unit) connects the measurement wavefront WM1 (measurement wavefront of region 1: first wavefront) and the estimated wavefront WM2 (estimated wavefront of region 2: second wavefront). (Do stitching). Thereby, the wavefront calculation unit 204 can calculate the measurement wavefront WM of all analysis regions including the region 1 and the region 2, that is, the transmitted wavefront or the reflected wavefront of the test optical system TO (optical element).

  Here, the processing by the wavefront estimation unit 203 will be described. The wavefront estimation unit 203 estimates the wavefront W of the test optical system TO by solving the nonlinear problem numerically. At this time, the physical model parameters of the measurement optical system (wavefront measuring apparatus 100) can be estimated simultaneously. The physical model parameters of the measurement optical system include parameters that contribute to the final spot image distribution generation, such as the wavefront of the illumination light, the intensity distribution, the shape of the optical element, the arrangement of the optical element, the lenslet array parameters, and the detector characteristics. It is. In addition to the wavefront W of the optical system TO to be estimated to be estimated, the wavefront estimation unit 203 also physically contributes to spot image distribution generation, such as the shape of the optical element, the arrangement of the optical element, and the refractive index and reflectance characteristics of the optical element. Model parameters can also be estimated.

  Preferably, the wavefront estimation unit 203 includes first processing means 203a that performs light propagation calculation based on the optical element (test optical system TO) and the physical model parameters of the wavefront measuring apparatus 100. The wavefront estimation unit 203 includes a second processing unit 203b that calculates a cost function based on data from the Shack-Hartmann sensor optical system SH (measurement unit) and a result of light propagation calculation. The wavefront estimation unit 203 includes a third processing unit 203c that determines a physical model parameter using, as an index, a cost function that is repeatedly calculated by changing the physical model parameter.

  In the present embodiment, for example, an estimation method such as a maximum likelihood method can be used for estimating the physical model parameters. In the present embodiment, the wavefront estimation unit 203 uses the measurement wavefront WM1 in the region 1 as the initial value of the measurement wavefront WM of the optical system TO to be estimated. The wavefront estimation unit 203 uses the measurement wavefront WM1 in the region 1 as an initial value, performs forward propagation calculation including light propagation calculation using the physical model parameters of the measurement optical system, and obtains a spot image IS that is an output of the detector array DA. Obtained by calculation. As the forward propagation calculation, methods such as geometric optical ray tracing, wave optics, and beamlet propagation calculation can be used. Further, based on the calculated spot image obtained in this way and the spot image IS obtained in the actual optical system, a likelihood that is an index of likelihood is calculated. As a likelihood function for calculating the likelihood, for example, Harrison H. et al. Barrett, Christopher Dainty, and David Lara, “Maximum-likelihood methods in wavefront sensing: stochastic models and likefund.” Opt. Soc. Am. A. 24, 391-414 (2007), a function considering various noise factors can be used.

  In the maximum likelihood method, forward propagation calculation (light propagation calculation) and likelihood function calculation are repeated while changing the measurement wavefront WM (estimated wavefront WM2) and physical model parameters. Thereby, the measurement wavefront WM (estimated wavefront WM2) and the physical model parameter with the highest likelihood are searched. Then, the measured wavefront WM (estimated wavefront WM2) and physical model parameters at the time when it is determined that the likelihood has converged to the maximum value are used as the estimated values of the measured wavefront WM (estimated wavefront WM2) and physical model parameters. As a search calculation of a physical model parameter that can take such maximum likelihood, a simulated annealing method or a Downhill simplex (Nelder-Mead) method is used. However, the present embodiment is not limited to this, and various optimization methods such as a Conjugate gradient method can be used.

  The wavefront measuring apparatus 100 (wavefront calculating unit 204) of the present embodiment calculates a measurement wavefront WM that is a measurement result of the wavefront W to be detected, so that the wavefront W to be detected is a large aberration wavefront having a large wavefront displacement, Even when a plurality of spots overlap each other, highly accurate wavefront measurement is possible. In addition, the wavefront measuring apparatus 100 (wavefront estimating unit 203) of the present embodiment uses the measured wavefront WM1 measured in advance with high accuracy as the initial value of the measured wavefront WM (estimated wavefront WM2). Thereby, compared with the case where the wavefront of all the areas | regions (area | region L1, L2) is estimated, time required for estimation can be shortened and estimation converges with high precision. As the spot image IS used for estimation, the spot image IS of only the region 2 may be used instead of the data of the entire region (regions L1 and L2). In this case, since the forward propagation calculation time in the wavefront estimation unit 203 can be shortened, the wavefront measurement can be further speeded up.

  According to the wavefront measuring apparatus 100 of the present embodiment, a high-precision optical element that generates a reference wavefront for calibration, which is necessary for measurement of a conventional large aberration wavefront, is not necessary. For this reason, the cost for designing, measuring, and manufacturing a highly accurate optical element can be reduced. As a result, it becomes possible to evaluate the wavefront of an optical element or optical unit having a wavefront with large aberration in a short time and at a low cost. Based on this measurement wavefront, it is possible to perform performance evaluation and unit adjustment in units of elements and units, and it is possible to provide a high-performance and low-cost wavefront measurement apparatus 100 (optical system). Also, an optical system that stores the measured wavefront of the optical system measured using the wavefront measuring apparatus 100 of this embodiment as data, and outputs images and data digitally corrected for aberrations using signal processing from the measured wavefront. Can be realized. An actual correction optical system can also be used for aberration correction. In this case, since it is not necessary to strictly manage the aberration of the optical system at the time of designing and manufacturing the optical system, it is possible to provide a lower cost optical system and an optical system incorporating the optical system. .

  In the present embodiment, the region determination method by the wavefront recovery region determination unit 201 is not limited to the method using the center of gravity detection results of the regions L1 and L2. For example, a condition that the main lobe does not overlap with the adjacent main lobe, that is, a condition that the distance d between the adjacent spot positions is a predetermined value or less may be used. As described above, the wavefront recovery region determination unit 201 can also determine the first region (region 1) and the second region (region 2) based on the distance d between adjacent spot positions. Here, where λ is the wavelength of the light source, NA is the numerical aperture of the lenslet, w is the diameter of the lenslet, and f is the focal length of the lenslet, the distance d between adjacent spot positions is given by the following equation (6): It is expressed as follows.

  The wavefront recovery region determination unit 201 may determine the first region (region 1) using the condition expressed by equation (6). For example, when λ = 0.53 μm, w = 150 μm, and f = 6 mm, d <52 μm. When λ = 0.532 μm, w = 150 μm, and f = 12 mm, d <104 μm. By determining an area that can be measured by the conventional SHWFS wavefront reconstruction algorithm based on such a standard, signal processing can be simplified, and therefore the measurement time can be shortened.

  Further, the wavefront recovery region determination unit 201 detects the center of gravity of the spot position as the region determination condition, and the incident angle of the light corresponding to the spot position (the angle of light incident on the encoding optical system 120) is within a predetermined angle. It may be used. As described above, the wavefront recovery region determination unit 201 can determine the first region (region 1) and the second region (region 2) based on the angle of light incident on the encoding optical system 120. For example, by setting the incident angle or less so that the incident angle characteristic of the sensor (encoding optical system 120) is greatly reduced, a measurement result that is less dependent on the sensitivity error of the sensor can be obtained.

  The wavefront recovery region determination unit 201 may use a design value (design data) of the wavefront measuring apparatus 100 including the optical system TO to be tested as the region determination condition. In this case, a region where a plurality of spots overlap or the wavefront recovery accuracy deteriorates can be predicted in advance using ray tracing or the like. By storing such information in advance, the wavefront recovery region determination unit 201 can perform region determination. As a result, the measurement time can be shortened.

  In the present embodiment, the configuration using the lenslet array MLA as the encoding optical system 120 for forming the spot image IS on the detector array DA is described. However, the present invention is not limited to this. As the encoding optical system 120, for example, an aperture plate having a plurality of apertures (apertures), a one-dimensional grating, or a two-dimensional grating may be used. When an aperture plate is used, a generally known Hartmann screen wavefront recovery algorithm can be applied to the wavefront reconstruction unit 202. When a one-dimensional grating or a two-dimensional grating is used, the wavefront reconstruction of the region 1 can be performed by applying the Ronchi test method, the FFT method, or the like to the wavefront reconstruction unit 202. These methods are obtained by linearly modeling the relationship between the observation data output from the detector array DA and the wavefront, and other similar methods can be applied to the wavefront reconstruction unit 202.

  In the wavefront measuring apparatus 100 of the present embodiment, an interferometer can be used as the encoding optical system. FIG. 11 is a block diagram of another form of the signal processing unit DSP in this embodiment, and shows the configuration of the signal processing unit DSP when the interferometer 140 is used as the encoding optical system.

  The interference fringe IF obtained by the interferometer 140 is output to the wavefront recovery region determination unit 301. The wavefront recovery region determination unit 301 determines a region 1 in which wavefront reconstruction is possible by normal interference fringe analysis. As the determination condition for the region 1, for example, a condition that the pitch of the interference fringe IF is 3 pixels (3 pixels) or more of the detector array MLA is used. As the interference fringe analysis, a geometric optical method, an FFT method, or the like can be used.

  The wavefront reconstruction unit 302 (first signal processing unit) calculates the measurement wavefront WM1 of the region 1 by performing interference fringe analysis (geometrical optical calculation) based on the interference fringes in the region 1. Subsequently, the wavefront estimation unit 303 (second signal processing unit) interfers with the measurement wavefront WM1 of the first region (region 1) calculated by the wavefront reconstruction unit 302 and the wavefront recovery region determination unit 301. Based on the fringe IF, the estimated wavefront WM2 of the second region (region 2) is calculated. Then, the wavefront calculation unit 304 (third signal processing unit) connects (performs stitching) the measurement wavefront WM1 (measurement wavefront of the region 1) and the estimated wavefront WM2 (estimated wavefront of the region 2), the region 1 and The measurement wavefront WM of the entire analysis region including the region 2 is calculated. By using such a wavefront measuring apparatus, the dynamic range of wavefront measurement can be expanded.

  Next, a wavefront measuring apparatus according to the second embodiment of the present invention will be described. The wavefront measuring apparatus 100 according to the first embodiment uses a relay optical system RYO that forms an image of the test light beam LB2 (such as a wavefront on the pupil plane of the test optical system TO) on the lenslet array MLA. On the other hand, the wavefront measuring apparatus 100a of the present embodiment replaces the relay optical system RYO with a simpler optical system in order to cope with measurement of a larger wavefront.

  FIG. 12 is a main part configuration diagram of the wavefront measuring apparatus 100a in the present embodiment. The wavefront measuring apparatus 100a includes a converging optical system CVO (enlargement / reduction optical system) instead of the relay optical system RYO. The converging optical system CVO enlarges or reduces the light beam diameter so that the test light beam LB2 enters the lenslet array MLA. In the present embodiment, the converging optical system CVO having a positive power that is reduced to such a size that the test light beam LB2 enters the lenslet array MLA is used. However, the present invention is not limited to this. It is possible to use an optical system that arbitrarily enlarges or reduces the transmitted light beam from the test optical system TO. In this case, in order to obtain the shape of the wavefront on the pupil (on the exit pupil) of the optical system TO to be measured, the wavefront W on the lenslet array MLA is measured, the measured wavefront WM is obtained, and then ray tracing or back propagation is performed. Thus, the wavefront of the pupil (exit pupil) may be obtained.

  When back propagation is performed in a state where the intensity distribution of the test light beam LB2 is not uniform, not only the measurement wavefront WM but also the lenslet array MLA based on the spot image IS (intensity distribution data) obtained from the Shack-Hartmann sensor optical system SH. The intensity distribution of the test light beam LB2 is used. Thereby, the precision of back propagation calculation can be improved. In this embodiment, an intensity distribution of the test light beam LB2 may be separately measured using an image sensor (not shown), and the measurement result may be applied to the back propagation calculation.

  FIG. 13 is a main part configuration diagram of another form of a wavefront measuring apparatus 100b in the present embodiment. As shown in FIG. 13, the wavefront W to be measured may be measured by directly irradiating the lenslet array MLA with the transmitted wavefront from the test optical system TO as the test light beam LB2. With such a configuration, measurement uncertainty caused by the relay optical system RYO can be reduced, and the cost of the optical system of the wavefront measuring apparatus (measurement system) can be reduced. For this reason, it becomes possible to implement | achieve a highly accurate and low-cost wavefront measuring apparatus.

  Next, a wavefront measuring apparatus according to Embodiment 3 of the present invention will be described. The wavefront measuring apparatuses 100, 100a, and 100b of the first and second embodiments are designed such that the size of the test light beam LB2 is equal to or smaller than the sizes of the lenslet array MLA and the detector array DA. On the other hand, in the wavefront measuring apparatus in the present embodiment, the test light beam LB2 may be larger than the size of the lenslet array MLA due to divergent light or the like.

  FIG. 14 is a main part configuration diagram of the wavefront measuring apparatus 100c in the present embodiment. The wavefront measuring apparatus 100c divides the entire surface of the test light beam LB2 into a plurality of regions while scanning the lens beam array MLA and the detector array DA (Shack-Hartmann sensor optical system SH) with respect to the test light beam LB2. An image IS is acquired. That is, in the wavefront measuring apparatus 100c, the Shack-Hartmann sensor optical system SH (measuring means) measures the light intensity distribution (spot image IS) by scanning the light beam transmitted or reflected by the optical element (test optical system TO). To do.

  Then, the measuring unit can measure the wavefront of the entire surface of the test light beam LB2 by connecting (sitting) a plurality of spot images IS divided into a plurality of regions. Further, slope angles and wavefronts of a plurality of regions may be calculated and connected to a region corresponding to the entire surface of the test light beam LB2. In addition, a plurality of spot images IS obtained while being divided into a plurality of regions may be separated into a spot image to which a conventional SHWFS wavefront reconstruction algorithm can be applied and a spot image to which wavefront estimation is applied. In this case, the entire wavefront can be estimated using the data of the spot image to which the remaining wavefront estimation is applied, with the wavefront reconstructed from the spot image to which the wavefront reconstruction algorithm is applied as an initial value.

  With such a configuration, it is possible to measure a wavefront of a test optical system having a large effective diameter or a test optical system having a negative power using a lenslet array MLA and a detector array DA of a finite size. Become. For this reason, a low-cost wavefront measuring apparatus (measuring system) can be realized.

  Next, a wavefront measuring apparatus according to Embodiment 4 of the present invention will be described. The wavefront measuring apparatuses 100 to 100c according to the first to third embodiments are configured to measure the wavefront transmitted through the test optical system TO with a single path. On the other hand, in this embodiment, the wavefront measuring apparatus is configured using a double-pass optical system.

  FIG. 15 is a main part configuration diagram of the wavefront measuring apparatus 100d in the present embodiment. The wavefront measuring apparatus 100d includes a beam splitter BS, and is configured to measure the transmitted wavefront of the optical system TO to be measured with a double-pass optical system. In this case, since the total length of the measurement optical system can be shortened, the size of the apparatus can be reduced. However, in general, an optical path through which light emitted from the light source LS passes through the test optical system TO and an optical path through which the light is reflected by a plane or spherical mirror (mirror MR) and passes through the test optical system TO are mutually connected. Is different. This optical path difference becomes a so-called retrace error. According to the configuration of the present embodiment, since the retrace error can be calculated as calibration data, the measurement accuracy of a compact double-pass optical system can be improved.

  FIG. 16 is a main part configuration diagram of a wavefront measuring apparatus 100e according to another embodiment of the present embodiment. As shown in FIG. 16, the wavefront measuring apparatus 100e includes a test optical system TO configured by a reflection optical system. In this case, the result of the measured wavefront can be obtained by converting the shape of the reflecting surface of the test optical system TO.

  According to each embodiment, it is possible to realize a wavefront measuring device with a wide dynamic range at low cost. A unit optical system or optical element included in an optical system such as a camera lens or a video lens may have a transmitted wavefront that deviates greatly from the reference spherical surface by itself, and is difficult to measure with the conventional method. By adopting the configuration of each embodiment, it is possible to measure the transmitted wavefront and the surface shape of such unit optical systems and optical elements with high accuracy and low cost. As a result, the performance of the unit optical system or the optical element alone can be guaranteed, which contributes to the realization of a low-cost and high-performance imaging optical system.

  Further, in each embodiment, by measuring physical parameters including the wavefront shape, it is possible to calculate parameters used for assembly adjustment of the optical unit. For example, an optimal arrangement position and orientation of the optical element that minimizes the aberration of the entire optical system can be obtained from the measured wavefront shape, surface shape, refractive index distribution, and the like. By assembling and adjusting the optical system based on the optimal arrangement position and orientation of such optical elements, it is possible to provide an optical system (an assembly adjustment apparatus for the optical system) with guaranteed optical performance.

  As described above, according to each of the embodiments, a wavefront measurement of an optical element having a large wavefront aberration is possible, and a highly accurate and low-cost wavefront measurement apparatus, a wavefront measurement method, an optical element manufacturing method, and an optical system are provided. Assembling and adjusting apparatus can be provided. As a result, it is possible to reduce the development cost and production cost of the optical element and the optical unit, and it is possible to realize high performance and low cost of the optical system.

  As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to these embodiment, A various deformation | transformation and change are possible within the range of the summary.

DESCRIPTION OF SYMBOLS 100 Wavefront measuring device 120 Encoding optical system 201 Wavefront recovery area determination part 202 Wavefront reconstruction part 203 Wavefront estimation part

Claims (20)

A wavefront measuring device for measuring a transmitted wavefront or reflected wavefront of an optical element,
Measuring means for measuring a light intensity distribution based on a light beam transmitted or reflected by the optical element;
Area determination means for determining the first area and the second area based on a plurality of spot positions in the light intensity distribution;
First signal processing means for calculating a first wavefront using a linear model based on information on the light intensity distribution of the first region;
Second signal processing for estimating a second wavefront by repeatedly performing light propagation calculation using the first wavefront as an initial value based on information on the light intensity distribution of the first region and the second region And a wavefront measuring device.   2. The signal processing apparatus according to claim 1, further comprising third signal processing means for calculating the transmitted wavefront or the reflected wavefront of the optical element by connecting the first wavefront and the second wavefront. Wavefront measuring device.   3. The wavefront measuring apparatus according to claim 1, wherein the second signal processing unit estimates the second wavefront by using optimization calculation of a wavefront parameter. The first signal processing means calculates the first wavefront using geometric optical calculation;
The second signal processing unit includes:
First processing means for performing the light propagation calculation based on physical model parameters of the optical element and the wavefront measuring device;
Second processing means for calculating a cost function based on the data from the measurement means and the result of the light propagation calculation;
4. The method according to claim 1, further comprising: a third processing unit that determines the physical model parameter by using a cost function repeatedly calculated by changing the physical model parameter as an index. 5. The wavefront measuring apparatus described.   5. The wavefront measuring apparatus according to claim 1, wherein the measuring unit includes a lenslet array and a detector array.   5. The wavefront measuring apparatus according to claim 1, wherein the measuring unit includes an aperture plate having a plurality of apertures and a detector array.   5. The wavefront measuring apparatus according to claim 1, wherein the measuring unit includes a one-dimensional grating or a two-dimensional grating, and a detector array.   The wavefront measuring apparatus according to claim 1, wherein the measuring unit is a Shack-Hartmann wavefront sensor.   The wavefront measuring apparatus according to claim 1, wherein the measuring unit is an interferometer.   The area determination unit determines the first area and the second area based on the plurality of spot positions detected in detection areas having a plurality of different sizes. The wavefront measuring apparatus according to any one of 1 to 9.   The said area | region determination means determines the said 1st area | region and the said 2nd area | region based on the distance between adjacent spot positions, The any one of Claim 1 thru | or 9 characterized by the above-mentioned. Wavefront measuring device.   The said area | region determination means determines the said 1st area | region and the said 2nd area | region based on the light ray angle which injects into the said measurement means, The any one of Claim 1 thru | or 9 characterized by the above-mentioned. Wavefront measuring device.   The wavefront according to any one of claims 1 to 12, wherein the region determination unit determines the first region and the second region using a design value of the wavefront measuring apparatus. Measuring device.   14. The wavefront measuring apparatus according to claim 1, wherein the measuring unit measures the light intensity distribution by scanning the light beam transmitted or reflected by the optical element.   The wavefront measurement apparatus according to claim 1, wherein the measurement unit measures a wavefront on an exit pupil of the optical element. A wavefront measurement method for measuring a transmitted wavefront or a reflected wavefront of an optical element,
Measuring a light intensity distribution based on a light beam transmitted or reflected by the optical element;
Determining a first region and a second region based on a plurality of spot positions in the light intensity distribution;
Calculating a first wavefront using a linear model based on information about the light intensity distribution of the first region;
Estimating the second wavefront by repeatedly performing light propagation calculation using the first wavefront as an initial value based on information on the light intensity distribution of the first region and the second region. A wavefront measuring method characterized by that.   The wavefront measurement method according to claim 17, further comprising a step of calculating the transmitted wavefront or the reflected wavefront of the optical element by connecting the first wavefront and the second wavefront.   The wavefront measurement method according to claim 16 or 17, wherein the plurality of spot positions are detected in detection areas having a plurality of sizes different from each other.   An optical element manufacturing method using the wavefront measuring method according to any one of claims 16 to 18.   An arrangement position or orientation of the optical element is calculated using the wavefront measurement method according to any one of claims 16 to 18, and assembly adjustment of the optical system is performed based on the arrangement position or orientation. An assembly adjustment device for an optical system characterized by the above.